Copper(II) Bromide Complexes: Crystal Structures, Magnetic Properties, and Hydrogen-Bond-Mediated Exchange

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper reports a the synthesis of a series of bromidocuprate(II) complexes with Dabco as a starting reagent (and generally present a a ligand or a counterion).  Full single structure determinations are provided for each along with magnetic data.  These all appear to be new crystal structures, none show up in my search of the Cambridge Structural Database.  The structures are complemented by insights from comparing refinements in IAM and NoSpherA2 models and modelling magnetic interactions.

The paper appears to have been hastily written and needs more proofreading.

1. I fell the title is incomplete as some of the compounds are bridging ligands and, hence, are not mononuclear.
2. Since the abstract is independent of the paper, the abbreviation Dabco should be defined.
3. The last paragraph of the Introduction belongs in results or conclusions.  The scope of the work should be outlined here and the compounds represented by boldface numbers should be clearly identified (at places in the manuscript these are not boldfaced).
4. Figure 3 and Figure 4 are not cited in the proper order in the text.  In addition, Figure 3 does not show what the figure caption claims.  If this is meant to be a unit cell packing diagram, the outline of the unit cell should be present.
5. In compound 5 the H2Dabco is not coordinated to the Cu(II), so should be left outside the brackets.  Referring to these as "chain-like structures" is a bit facile.  These appear to be stacks of symmetrically bridged dinuclear complexes with longer semicoordinate Cu-Br bonds linking the complexes.  It very well could be isostructural to the chloride analog (CSD Refcode: ICAZIZ), but basic crystallographic data is not present in the main paper.  I would suggest that basic crystallographic information such as crystal system, space group and unit cell parameters to Table 1.  More generally, I find the structure descriptions to be terse.  More insightful descriptions would be helpful, as well as comparisons to related structures--particularly any chloride analogs.  
6. In contrast, experimental procedures are extremely detailed.  I fell the paper would benefit from a more concise description of these procedures with the full details available in supplementary materials.
7. A thorough effort should be made to correct typographical errors throughout the manuscript.  For example, there is a space missing before the word "and" in reference 19.

    

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses in the attachment. The corresponding revisions/corrections are highlighted in the re-submitted files.

The title was slightly modified. In the introduction, the search of the CSD database for known copper(II)-bromide-Dabco complexes was summarised. Compound 5 was thoroughly described and compared with the isostructural Cl analogue. The conclusion was slightly changed. Figures 4 (slightly), 5 (slightly), and 8 (completely), along with their captions, were changed.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This study synthesized seven new mononuclear copper(II) bromide complexes, six of which incorporate 1,4-diazabicyclo[2.2.2]octane as a ligand. Single-crystal X-ray diffraction data were refined using both the conventional Independent Atom Model (IAM) and the non-spherical atom approach via NoSpherA2, with the latter significantly improving the description of hydrogen atom positions and yielding C–H and N–H bond lengths closer to neutron diffraction values. Magnetic property investigations through temperature-dependent susceptibility and field-dependent magnetization measurements (analyzed via molecular field approximation) revealed that magnetic interactions between copper(II) centers are dominated by intermolecular exchange pathways rather than Cu···Cu distances alone. Despite comparable Cu···Cu separations, complexes lacking NH···Br hydrogen bonds (compounds 2 and 4) exhibited only weak antiferromagnetic interactions (effective below 30 K), while compound 7—featuring NH···Br hydrogen bonds—showed much stronger coupling persistent up to 150 K. Notably, NH···N hydrogen bonds (compound 2) and bridging Dabco ligands (compound 4) did not mediate efficient magnetic exchange. This work highlights the critical role of hydrogen-bond topology and three-dimensional connectivity in regulating magnetic behavior, advancing the understanding of structure–property relationships for the rational design of functional magnetic materials and potential quantum information processing candidates. Before publication, some minor issues need to be taken into account：

1. The main text indicates that the Cu²⁺ in compound 7 has a four-coordinate distorted tetrahedral geometry (τ₄ = 0.82), while most other complexes have a five-coordinate trigonal bipyramid (τ₅ = 0.74 - 1.0). Is this difference in coordination mode directly related to the amount of HBr in the reaction system and the solvent type (e.g., MeOH vs ACN)?
2. In the introduction section of the main body of the manuscript, it was mentioned that DFT calculations are commonly used to explain hydrogen bond-mediated magnetic interactions. However, no relevant calculation results are presented throughout the entire text. Has any other related supplementary calculation been provided to support the electron transfer mechanism of the NH...Br hydrogen bond?
3. Compounds 1-3 in the main text are synthesized by electrochemical method, compound 4 by solvothermal method, and compound 7 by stirring evaporation method. What is the basis for choosing different synthesis strategies? Has a unified synthesis method been attempted to eliminate the interference of preparation process on the structure and magnetism of the complexes?
4. The antiferromagnetic coupling of compound 7 remains effective above 150 K, while compounds 2 and 4 only show this effect below 30 K. Is this temperature-dependent difference related to the thermal stability of hydrogen bonds?
5. The main text points out that compound 2 contains NH···N hydrogen bonds but only shows weak antiferromagnetic interaction, while the NH···Br hydrogen bonds of compound 7 mediate strong coupling. Is the difference in electronegativity and atomic radius between Br⁻ and N atoms leading to different "magnetic transfer efficiency" of hydrogen bonds?
6. Some recent relevant literatures are suggested for citations: Adv. Sci. 2025, 12, e15170 (https://doi.org/10.1002/advs.202515170); Chem. Sci.,2025, 16, 22021–22028 (DOI: 10.1039/d5sc04977f); Sci. China Chem. (2026). (https://doi.org/10.1007/s11426-025-2992-0).

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses in the attachment. The corresponding revisions/corrections are highlighted in the re-submitted files.

The title was slightly modified. In the introduction, the search of the CSD database for known copper(II)-bromide-Dabco complexes was summarised. Compound 5 was thoroughly described and compared with the isostructural Cl analogue. The conclusion was slightly changed. Figures 4 (slightly), 5 (slightly), and 8 (completely), along with their captions, were changed.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

In this paper a series of copper(II) bromide complexes are studied via crystal structures magnetic properties, and hydrogen-bond-mediated exchange

Seven crystal structures are determined and the refinements as reported in the cif files are successful. When checking the cif files, I obtained a new checkcif file for structure 2 using the submitted cif file and  found that it was different from that submitted by the authors. Indeed it had two A Alerts. Structures 5 and 6 were not  provided with a checkfile obtained from the checkcif program and these need to be provided. In all cif files, details of the H-bonds should be provided. All checkcif files  submitted by the authors need to be obtained from the cifs submitted and contain no A or B alerts.

In the text, the structures of the complexes are well described and the figures are very clear. When the hydrogen bonds are described in the text,  only the donor-acceptor (D-A) distances are given. Further details such as D-H, H…A distances and D-H…A angles should be provided either in the text or in a Table.

The distances and angles in the copper coordination spheres should be provided in a Table in Supplementary Material and any variations discussed in the text. While  the τ values are given in the text, one would have liked to see more details of  the distortions from ideal symmetry as indicated by bonds and angles.

When summarising the wide range of structures involving the dabco (lsection 2.1.8, it would be useful to compare with other dabco structures in the literature.

Figure 5 Thee ligands need to be made complete rather than truncated at the edges

Having described the structures, the paper then compares refinement parameters obtained using IAM and HAR methods which lead to interesting comparisons with the x-ray results. These refinements are well described.

This paper is well written and the work is interesting. 

 

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses in the attachment. The corresponding revisions/corrections are highlighted in the re-submitted files.

The title was slightly modified. In the introduction, the search of the CSD database for known copper(II)-bromide-Dabco complexes was summarised. Compound 5 was thoroughly described and compared with the isostructural Cl analogue. The conclusion was slightly changed. Figures 4 (slightly), 5 (slightly), and 8 (completely), along with their captions, were changed.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have quite rapidly(!) responded to my concerns. I agree with the changes.  I would like to see basic crystallographic information in the main paper, but if that is not journal policy I won't push that point further.  I have no further objectcions.